I wouldn't bother doing a gti conversion all j4 engines are shaaaged these days & go for peanuts! you could get yourself a j4 for parts and get a low mileage tu5jp4 engine (206, 307 1.6 16v engine's) cheapish and then convert it.

cost about £400 in total but you'll get a low mileage 16v, is a bit of a pain to convert the jp4 but u only have to change valve springs, cams, inlet & drill new holes for studs and change over the oil filter set-up from a j4 block.

It's what i have done, in a saxo but the theory's still the same mate, check my blog if u want pic's etc there will be a lot more on there about the conversion in the next few days. I'm hoping for 130-140bhp, fready666 on here got over 150hp with the same set-up! So compared to a gti block you would have a much better & newer base to start with and bigger inlet valves. You'd need a gti loom+ecu too so if u do that you'll be better off buying a gti block etc for parts.

Or u could ignore that and mod the rallye block as it should have a good bit of life in it yet! Especially if it's had regular services.

What car's have u had before mate?? Small french hatchbacks are the way forward if u ask me!